1. Field of the Invention
This invention relates to the production of resistant starch and products formed therefrom and; in particular, to methods of improving the yield of resistant starch in a dextrin reaction by, for example, adding an effective amount of an alcohol component during the acidification process.
2. Background
Starch is a naturally occurring polymer made up of anhydroglucose units and is obtained by processing plant materials. The plant materials from which starch is derived include, but are not limited to corn, wheat, potato, cassava, and rice. Of these plant materials, corn is one of the most commonly used sources for starch in North America.
Starch is used in a wide number of applications, both industrial and private. These uses include food products, papermaking, corrugated boxes, glue, baby powder, and textiles. Food products produced from starch are varied and include dextrose, corn syrup, high fructose corn syrup, crystalline dextrose, fructose, xanthan gum, citric acid, lactic acid, sorbitol, lysine, threonine, riboflavin, and distilled spirits.
An additional product is resistant starch, which is a name given to starches which resist digestion in the human body. Resistant starch is an important part of the human diet and has been shown to promote intestinal regularity, moderate post-prandial blood glucose levels, and lower serum cholesterol and triglyceride levels. Resistant starch can be obtained by the manufacture of pyrodextrins, which are made at low moisture and low pH by the action of heat and an acid catalyst, such as hydrochloric acid, to produce a slightly yellow powder. Typically, the acid catalyst is added through atomization and spraying of a water-diluted acidic solution containing the acid.
Starch consists primarily of alpha 1,4- and alpha 1,6-glucosidic linkages. Resistant starches can be prepared by heat treating a starch at a high temperature. However, the mechanism of resistant starch development is complex. During the initial stages of dextrinization, acid-catalyzed hydrolysis occurs. This is followed by a recombination of the fragments to form branched structures. Specifically, the dextrinization process converts a portion of the normal alpha 1,4-glucosidic linkages to random 1,2-, 1,3-, and 1,4-alpha or beta linkages. These chemical changes are described in “Modified Starches: Properties and Uses”, O. B. Wurzburg, CRC Press, Inc. 1986, pp. 33-34.
These branched structures containing the new bonds are not digestible by maltase and isomaltase in the small intestine. This is because the human digestive system effectively digests only alpha 1,4-linkages. The majority of the resistant starch reaches the large intestine, and thus is characterized as a “dietary fiber,” defined as components of plant material in the diet that are resistant to digestion by enzymes produced by humans in the small intestine.
In the preparation of resistant starch in dextrin, heat, acid, and time are employed to rearrange the molecular structure to form indigestible branched structures. This also results in the development of color attributed to the carmelization reactions. Carmelization reactions are a diverse group of dehydration, fragmentation, and polymerization reactions whose reaction rates are dependent on temperature and pH (See, “Sugar Chemistry”, R. S. Shallenberger and G. G. Birch, AVI, 1975, pp. 167-177). The dextrinized starch will typically take on a yellow color depending on the specifics of the reaction conditions.
It is preferable that the finished dextrinized product be almost colorless in solution due to the application of this product in the food industry. In the majority of cases, any color developed in the dextrinization process is not desirable in the final product and is largely removed through subsequent, and costly, decolorization steps. In order to minimize the costs associated with color removal, a dextrinized starch with minimal color development would be advantageous.
However, development of resistant starch in dextrin typically occurs contemporaneously with color development as the dextrinization reaction progresses. Also, prior to dextrinization and during the acidification process when a water-diluted acidic solution is atomized and sprayed on the starch, localized concentrations of acid lead to charring of the starch, thus contributing to color development in addition to carmelization reactions. The object, however, is to manufacture a dextrin with the greatest degree of resistant starch possible while minimizing the objectionable color formation.
In actual operation, there are two tests that measure color. The first test is a whiteness meter and is run on dry dextrin samples. An example of a whiteness meter is a Kett Electric Laboratory Whiteness meter, model C-1, with a range of 0 to 100, where 0 represents the darkest and 100 represents the whitest points on the scale. The second test employs a spectrophotometer to measure the color of a dextrin sample dissolved in water in the form of a slurry at ten percent dry solids. In the second test, higher levels of absorbance indicate a more colored product. The absorbance is monitored by a spectrophotometer at wavelengths of 420 and 720 nm, with the difference being multiplied by ten and recorded as the color.
When a process to manufacture resistant starch is designed, the design parameters take into account both a whiteness value and an absorbance color value of the dextrin because the decolorization steps such as carbon treatment can only treat a certain amount of color bodies before recharging. In order to keep costs at economic levels, the dextrinized starch must not be too colored. For example, it has been found that by maintaining a whiteness value about 65 and an absorbance color value of 20 or lower, the subsequent decolorization steps result in an end product that is economically viable.
The object of the dextrinization process is to produce a dextrin containing the highest yield of resistant starch possible while maintaining a whiteness value above 65 and a spectrophotometer color below 20. Although other whiteness and absorbance color targets can be used, these targets require either more or less equipment to remove the color depending on whether it is less colored (less equipment and materials) or more colored (additional equipment and materials).